The present invention relates to a solid-state imaging device including a light-receiving section such as a photoelectric conversion section.
A solid-state imaging device such as a MOS image sensor, for example, typically employs a structure including a semiconductor substrate with light-receiving sections (photoelectric conversion sections such as photodiodes) provided thereon, and various films such as light-blocking patterns and wiring patterns provided in multiple layers on the semiconductor substrate. Downsizing such a solid-state imaging device will inevitably shorten the inter-pupillary distance of the camera lens, thereby increasing the amount of oblique light component being incident on a pixel array section (an imaging area) in which a plurality of pixels are provided in a two-dimensional arrangement, especially, on a peripheral portion thereof. For each pixel, as the angle of incidence of light is greater, light is more blocked by wires, and the like, thus decreasing the amount of light to be directly incident upon the light-receiving surface. Therefore, it is difficult to maintain a high level of image quality.
Many of the current solid-state imaging devices employ an on-chip microlens for each pixel for the purpose of improving the light condensing rate. However, in a peripheral portion of the imaging area where an increased amount of light is incident from an oblique direction, the center of light condensation by the condensing lens is shifted from the center of the light-receiving section. This reduces the rate of light condensation onto the light-receiving section, thus deteriorating the sensitivity. The degree of sensitivity deterioration increases from the central portion of the imaging area toward the peripheral portion thereof.
In view of this problem, a conventional solid-state imaging device proposed in the art employs a structure where the condensing lenses in the imaging area are shifted and only the uppermost wiring layer is shifted (see, for example, Japanese Patent No. 3709873).
FIG. 14 is a cross-sectional view showing an important part of the structure of this conventional solid-state imaging device.
As shown in FIG. 14, light-receiving sensor sections 101 are formed in an upper portion of a semiconductor substrate 100, and first to third wiring layers 103 to 105 are formed on the semiconductor substrate 100 and the light-receiving sensor sections 101 with an interlayer insulating layer 102 being interposed therebetween. A color filter 107 is formed on the uppermost third wiring layer 105 with a flattening film 106 being interposed therebetween.
In the conventional solid-state imaging device having such a structure, the condensing lenses (not shown) are arranged so that the centers thereof are at a constant pitch across the entire pixel area. In the peripheral portion of the imaging area, the arrangement of the condensing lenses with respect to the light-receiving sensor sections 101 are shifted in the horizontal direction or in the vertical direction from the peripheral portion of the imaging area toward the central portion thereof as indicated by the arrow b. Only with the shifting of the condensing lenses, incident light a may be blocked by the uppermost wiring layer, thus deteriorating the sensitivity. In order to prevent this, only the uppermost third wiring layer 105, which is farthest away from the light-receiving sensor sections 101, is shifted in the peripheral portion of the imaging area.
Thus, with the structure where only the uppermost wiring layer is shifted only in one of the horizontal direction and the vertical direction, it is possible, despite the simple connection/layout of wiring layers, to prevent oblique incident light in the peripheral portion of the imaging area from being intercepted by the uppermost wiring layer, thus improving the rate of light condensation onto the light-receiving section and preventing the sensitivity deterioration.
Downsizing a solid-state imaging device will inevitably shorten the inter-pupillary distance of the camera lens, thereby increasing the angle of incidence of light in the pixel array section (the imaging area) in which a plurality of pixels are provided in a two-dimensional arrangement, especially, in the peripheral portion thereof, with the increased angle of incidence being about 25° to 35° with respect to the vertical direction to the substrate surface. Therefore, just shifting the uppermost wiring layer as in the conventional solid-state imaging device is not sufficient for ensuring a desirable sensitivity, with the presence of the lower wiring layers intercepting the incident light to significantly deteriorate the sensitivity.
Where not only the uppermost wiring layer but also the lower wiring layers are to be shifted, it is difficult to realize a solid-state imaging device having such a layout that all elements of wiring layers are shifted because the wiring layers are electrically connected to each other via contacts.